The present invention relates generally to aortic diverters for temporary or permanent placement in the aorta in order to divert embolic material away from the arteries that carry blood to the brain, i.e., the carotid or cerebral arteries (including the brachiocephalic trunk, the left common carotid, and the left subclavian; Anne R. Agur, Grant""s Atlas of Anatomy 52 (9th ed., Williams and Wilkins 1991) (1943) (this and all other references cited herein are expressly incorporated by reference as if set forth in their entirety in this disclosure)). More particularly, the invention relates to aortic diverters placed within the ascending aorta, either temporarily or permanently, such that embolic debris entering the aorta are carried through or past the diverter and past the carotid arteries, thus being diverted away from cerebral blood vessels. The present invention also relates to methods of protecting patients against cerebral embolization by using aortic diverters.
Preventing emboli from entering the carotid arteries- (i.e., the brachiocephalic, the left common carotid, and the left subclavian) by way of the aorta reduces the incidence of ischemic stroke. Emboli in the aorta come from several sources. These sources include: 1) aortic atheroma which detaches from the wall of the aorta due to various reasons including incising, clamping, and/or clamp release of the aorta during surgery (see, Barbut et al., xe2x80x9cCerebral Emboli Detected During Bypass Surgery Are Associated With Clamp Removal,xe2x80x9d Stroke, 25(12):2398-2402 (1994)); 2) thrombus which forms in the right atrium resulting from atrial fibrillation; 3) thrombus which forms on ventricular assist devices; 4) venous thrombus which passes into the left ventricle through a patent foramen ovale or other arteriovenous shunt; and 6) other less common sources.
There are a number of known devices designed to filter blood (see, e.g., Barbut et al., International Application No. PCT/US97/12751, and Barbut et al., U.S. Pat. No. 5,662,671), but no known devices designed to divert or redirect emboli past the carotid arteries. Using careful surgical techniques, the chance of an embolic event causing harm to the patient by way of cerebral embolization is so low that emboli managing devices have not been considered. Thus, there are no known solutions to minimizing the probability of cerebral embolization; except for reducing the amount of emboli released into the blood stream by careful handling of blood vessels.
On the venous side of the circulatory system, implantable vena cava filters reduce the incidence of pulmonary embolism, but they only trap large emboli, and they have a tendency to become clogged as they accumulate material. For example, Cottenceau et al., U.S. Pat. No. 5,375,612 discloses a blood filter intended for implantation in a blood vessel, typically in the vena cava. This device comprises a zigzagged thread wound on itself and a central strainer section to retain blood clots. Another example is Lefebvre, French Patent No. 2,567,405, which discloses a blood filter for implantation by an endovenous route into the vena cava. The filtering means may consist of a flexible metallic grid, a flexible synthetic or plastic grid, a weave of synthetic filaments, or a non-degradable or possibly biodegradable textile cloth.
There are very few intravascular devices designed for arterial and especially aortic filtration, much less diversion. A filter that functions in arteries must address additional concerns because of the hemodynamic differences between arteries and veins. Arteries are much more flexible and elastic than veins and, in the arteries, blood flow is pulsatile with large pressure variations between systolic and diastolic flow. These pressure variations cause the artery walls to expand and contract. Thus, filters and diverters must be able to expand and contract along with the lumen of the aorta to which they may be anchored.
The problem of preventing emboli from reaching the cerebral vasculature has thus far not been adequately addressed. Therefore, a need exists for new devices and methods to prevent embolic material from entering the carotid/cerebral arteries, while maintaining peripheral blood flow from the heart to the descending aorta.
The present invention relates to aortic diverters and methods of diverting or redirecting emboli away from the carotid arteries to prevent cerebral embolization. The invention includes safe aortic diverters positionable in the ascending aorta in order to divert embolic material of all sizes away from the carotid arteries, thereby washing emboli downstream into the thoracic and peripheral vasculature. The devices of the present invention are adapted to be placed in the ascending and transverse aorta in order to divert embolic material away from the carotid arteries. This embolic matter includes but is not limited to atheromatous fragments or material, thrombus, globules of fat, air bubbles, clumps of bacteria and/or other foreign matter, tumor cells, or any other bits of tissue. The aortic diverters of the present invention can be placed surgically, endoscopically or percutaneously, and either permanently or temporarily.
In one embodiment of the invention the aortic diverter includes two components. The first component is a hollow tube, which is substantially cylindrical, conical or frustoconical in shape. The hollow tube is an appropriate size to fit within the lumen of the ascending aorta. The proximal end of the hollow tube is adapted to fill the lumen of the aorta so that substantially all blood entering the ascending aorta from the heart must travel through the hollow tube in order to continue past the ascending aorta and into the other arteries leading to the rest of the human body. The second component is an anchoring mechanism for securing the hollow tube to the lumen of the aorta.
In another embodiment the aortic diverter also includes two components. The first component is a hollow tube, which is substantially cylindrical, conical or frustoconical in shape. The hollow tube is an appropriate size to fit within the lumen of the ascending aorta. The proximal end of the hollow tube is adapted to fill the lumen of the aorta so that substantially all blood entering the ascending aorta from the heart must travel through the hollow tube in order to continue past the ascending aorta and into the other arteries leading to the rest of the human body. The second component is a sleeve secured to the proximal end of the hollow tube. The sleeve can be substantially rigid and circumferentially sized to frictionally anchor the hollow tube to the lumen of the aorta.
In another embodiment, the aortic diverter is a flat, planar, snowshoe device that can be placed across the apex of the aorta in order to prevent emboli from flowing into the carotid arteries. The snowshoe diverter comprises a planar tongue and a handle, and can also include supports or legs mounted on either or both sides of the tongue. The handle is attached to the proximal end of the tongue for convenient connection to an introducing device such as a cannula, and is also useful for easy orientation and placement of the snowshoe diverter within the aorta. The handle itself can be hollow, thus acting as a cannula to supply filtered blood to the carotid arteries as well as the descending aorta. The hollow cannulated handle can be attached to the tongue such that blood flowing out of the handle and into the aorta is partitioned by the tongue to flow either anterior or posterior the tongue. Alternatively, the cannulated handle can be attached to the tongue so that all blood flowing out of the handle and into the aorta flows anterior the tongue. Alternatively, the cannulated handle can be attached to the tongue so that all blood flowing out of the handle and into the aorta flows posterior the tongue. Alternatively, the handle can be solid with no lumen for blood flow. The handle can also be flexible and bendable in order to move the handle out of the way of the surgeon. The tongue of the snowshoe diverter has a compliant framework that allows conformance with naturally irregular interval wall structures within the aorta. The framework allows the size of the tongue to be reduced allowing for introduction through small incisions, thus minimizing aortic trauma. Thus, the tongue can be rolled or folded up in any direction or manner. The framework can comprise rings that are circular or oval. Alternatively, the framework can be a figure xe2x80x9c8xe2x80x9d suspension frame. The tongue also has a thin, compliant membrane that is impermeable to emboli. The membrane can be made of a mesh material that may be cotton based, Teflon, nitinol, urethane or polyurethane, any combination of the above, or a combination of the above along with wire. Alternatively, the tongue can be made of material that is impermeable to blood, but have one or more way valves allowing unidirectional blood flow. The tongue can be flexible and/or elastomeric, thus enabling the tongue to be rolled or folded up in any direction or manner. The tongue can be amoeba shaped, curved or billowed, tapered, or a combination thereof.
The methods of the present invention relate to the prevention of cerebral embolization. Cerebral embolization can occur when emboli found in the bloodstream are carried to the brain and become lodged in the smaller blood vessels of the brain, thus obstructing blood flow to an area of the brain, which can result in a stroke. One way of protecting patients against cerebral embolization is by preventing emboli from reaching the smaller blood vessels in the brain.
In one method of the invention an aortic diverter is provided. The aortic diverter is inserted into the aortic arch in the region of the carotid arteries. The surgeon secures the aortic diverter to the lumen of the aorta so that the proximal end of the aortic diverter extends upstream of the brachiocephalic trunk while the distal end of the aortic diverter extends downstream of the left subclavian artery. In the uncommon case where the carotid arteries directly connected to the aortic arch are just the left and right branch of the brachiocephalic trunk (see Anne R. Agur, Grant""s Atlas of Anatomy 52 (9th ed., Williams and Wilkins 1991) (1943) (incorporated herein by reference)), the distal end of the aortic diverter extends downstream of the left brachiocephalic trunk. With the aortic diverter placed in the ascending aorta in such a manner, emboli entering the ascending aorta will necessarily have to flow through the aortic diverter and exit the distal end of the aortic diverter downstream of the carotid arteries, thus reducing the likelihood that emboli will reach the openings leading into the carotid arteries.
In another method the surgeon provides an aortic diverter comprising a planar filter material which is impermeable to emboli but not to blood. The surgeon inserts the filter material into the aortic arch in the region of the carotid arteries. The surgeon secures the filter material to the aortic lumen so that it completely covers all of the openings leading from the aorta into the carotid arteries such that blood flowing into the carotid arteries is filtered of embolic material. The embolic material is not trapped on the filter but is washed downstream of the left subclavian artery or the left brachiocephalic trunk by the stream of blood rushing through the aorta into the peripheral vasculature.
In another method the surgeon provides an aortic cannula. The surgeon then penetrates the wall of the aorta with the aortic cannula, which can have an inflatable balloon occluder concentrically disposed on its distal end. The aortic cannula is sutured to the wall of the aorta to prevent loss of blood. The balloon occluder can be inflated to prevent back-flow of blood towards the region of the heart. The surgeon then provides the snowshoe diverter previously described. The surgeon then inserts the snowshoe diverter through the aortic cannula and into the aortic arch in the region of the carotid arteries, thus preventing emboli from flowing into the carotid arteries. Alternatively, the snowshoe diverter can be integral with the aortic cannula and disposed on the distal end of the aortic cannula. The surgeon then provides a blood-return cannula. If the handle of the snowshoe diverter is hollow (i.e., cannulated), the surgeon can connect the blood-return cannula to the handle of the snowshoe diverter such that it is in fluid communication with the handle. If the handle of the snowshoe diverter is not hollow, then the surgeon can connect the blood-return cannula to the aortic cannula such that it is in fluid communication with the aortic cannula. Alternatively, the surgeon can insert the blood-return cannula through the wall of the aorta either upstream or downstream of the point of insertion of the aortic cannula. When protection from cerebral embolization is no longer necessary, the surgeon removes the snowshoe diverter from the aorta.
In another method, an aortic cannula with a snowshoe aortic diverter attached to its distal end is introduced. The aortic cannula is inserted through the wall of the aorta and the snowshoe diverter is positioned in the region of the carotid arteries. The aortic cannula can be inserted through the wall of the aorta while the snowshoe diverter fully deployed. Alternatively, the snowshoe diverter can be hidden inside the lumen of the aortic cannula until after the aortic cannula is inserted through the wall of the aorta. The snowshoe diverter can then be deployed and positioned over the carotid arteries. The snowshoe diverter extends over all of the openings leading into the carotid arteries. The aortic cannula is sutured to the wall of the aorta to prevent loss of blood. A cardioplegia cannula comprising an opening in its distal end is then introduced. The cardioplegia cannula also has an inflatable balloon occluder concentrically mounted around its distal end. The cardioplegia cannula is inserted through the wall of the aorta and sutured to the wall of the aorta to prevent loss of blood. The balloon occluder is inflated to prevent all fluid flow downstream thereof, and then cardioplegia solution is delivered to the heart through the opening in the distal end of the cardioplegia cannula. Blood from a bypass machine is introduced into the aorta through aortic cannula. Blood flowing out of the distal end of the cannula and into the aorta can be partitioned by the snowshoe diverter such that some of the blood flows to the carotid arteries superior to the snowshoe diverter while the rest of the blood flows anterior the snowshoe diverter and toward the descending aorta and peripheral vasculature. Alternatively, the snowshoe device can be attached to the distal end of the aortic cannula in such a way as to divert substantially all blood exiting the distal end of the cannula to either the carotid arteries or the peripheral vasculature.
In another method the surgeon provides an aortic diverter, which is a substantially cylindrical, conical or frustoconical hollow tube comprising a wall that is impermeable to emboli. The hollow tube is substantially flexible, is in a compressed state, and is releasably carried by an intravascular catheter for percutaneous delivery into the aorta. When deployed, the hollow tube allows blood to flow through the tube, and the proximal end of the hollow tube is circumferentially sized to completely fill the lumen of the aorta. The surgeon introduces the intravascular catheter containing the compressed aortic diverter into the vascular system. The surgeon advances the intravascular catheter into the aortic arch to the region of the carotid arteries. The surgeon deploys the aortic diverter so that the aortic diverter radially expands to contact the lumen of the aorta. In the fully deployed state, the proximal end of the aortic diverter should completely fill the lumen of the aorta and should extend upstream of the brachiocephalic trunk. The distal end of the aortic diverter should extend downstream of the left subclavian artery (or the left brachiocephalic trunk in those patients having this as the most downstream carotid artery) so that when emboli exit the distal end of the aortic diverter, they are downstream of the carotid arteries, thus reducing the likelihood that they will reach the openings leading into the carotid arteries. The surgeon then secures the aortic diverter to the lumen of the aorta, either by friction of contact or by other means discussed herein.
The present invention addresses the dangers associated with cerebral embolization. Specifically, embolization contributes significantly to problems such as stroke, lengthy hospital stays, and, in some cases, death.
Embolic material, which has been detected at 2.88 mm in diameter, will generally range from 0.02 mm (20 xcexcm) to 5 mm, and consists predominantly of atheromatous fragments dislodged from the aortic wall and air bubbles introduced during dissection, but also includes platelet aggregates which form during cardiac surgery, thrombus in general, globules of fat, clumps of bacteria and/or other foreign matter, tumor cells, or any other bits of tissue. These emboli enter either the cerebral circulation or systemic arterial system. Those entering the cerebral circulation obstruct small arteries and lead to macroscopic or microscopic cerebral infarction, with ensuing neurocognitive dysfunction.
It is an object of the present invention to eliminate or reduce the incidence of cerebral embolization. The present invention is intended to divert emboli away from the carotid arteries, which direct blood to the brain. This diversion prevents strokes, which can lead to lengthy hospital stays, damage to the brain, and sometimes death. The present invention is particularly suited for those who are at high risk of suffering from cerebral embolization, such as elderly patients and those who have atheromatosis, as well as those patients undergoing cardiac surgery, which has been shown to result in the release of emboli into the bloodstream. See, for example, Barbut et al., xe2x80x9cCerebral Emboli Detected During Bypass Surgery Are Associated With Clamp Removal,xe2x80x9d Stroke, 25(12):2398-2402 (1994).
As for the devices, one object is to provide safe and reliable devices that are easy to manufacture and use. A further object is to provide devices that may be used in the aorta, and especially in the ascending aorta. Yet another object is to provide devices that will reduce the likelihood of cerebral embolization, especially in those patients who are at high risk for cerebral embolization. Yet another object is to provide devices that can be introduced into the aorta and secured to the lumen of the aorta with minimal trauma to the patient.
The devices disclosed herein have the following characteristics: they can withstand high arterial blood flow rates for an extended time; they can expand and contract with the wall of the aorta; they can be made of a monolithic molded material that is impermeable to blood as well as emboli, such as Teflon impregnated with an anti-thrombogenic coating or nitinol impregnated with an anti-thrombogenic coating, or they can be made of material that is impermeable to emboli and not blood, such as a mesh, a woven material, or a thin polymer; they can be biodegradable; they can include openings on their walls of any shape or predetermined pattern, wherein the openings are covered in material that is impermeable to emboli; they can be introduced surgically, endoscopically, or percutaneously with cannulas or intravascular catheters introduced through the femoral artery, subclavian artery, brachiocephalic artery, or a cut-down to the abdominal aorta; they can be left in the aorta permanently or temporarily; they can be secured to the lumen of the aorta through various mechanisms including sutures, surgical clips, hooks, adhesive material, substantially rigid sleeves, or frictional engagement; they can be flat, conical, frustoconical, or cylindrical; they can be radially self-expanding or expanded mechanically; they can be substantially rigid or substantially flexible like a xe2x80x9cwindsock;xe2x80x9d and they can be sized to fit vessels of varying sizes.
As for the methods of this invention, an object is to prevent cerebral embolization. The methods of this invention can be employed on various patients, especially those at high risk for cerebral embolization, in order to reduce the incidence of cerebral embolization, which can lead to neurologic or cognitive complications and death. Another object is to temporarily or permanently divert emboli away from the carotid arteries by forcing emboli downstream of the openings leading from the aorta into the carotid arteries. Another object is to provide a method for eliminating or minimizing cerebral embolization during invasive cardiac procedures. Yet another object is to provide a method of introducing an aortic diverter intravascularly or with a cannula for minimal trauma to the patient.